Decabromodiphenyl oxide (deca) and decabromodiphenylethane (deca-DPE) are commercially available materials widely used to flame retard various polymer resin systems. The structure of these materials is as follows:

One of the advantages of using deca and deca-DPE in polymer resins that are difficult to flame retard, such as high-impact polystyrene (HIPS) and polyolefins, is that the materials have a very high (82-83%) bromine content. This allows a lower load level in the overall formulation, which in turn serves to minimize any negative effects of the flame retardant on the mechanical properties of the polymer.
Despite the commercial success of deca, there remains significant interest in developing alternative halogenated flame retardant materials that are equally or more efficient, not only because of economic pressures but also because they may allow lower flame retardant loadings, which in turn may impart improved performance properties. Improved properties, such as non-blooming formulations, or better mechanical properties can potentially be met by producing polymeric or oligomeric flame retardant compounds. These types of materials would become entangled in the base resin polymer matrix, depending on the compatibility, and hence should show fewer tendencies to bloom.
There are a number of commercially available flame retardant materials that can be considered oligomers or polymers of halogenated monomers. Examples of these monomers include tetrabromobisphenol A (TBBPA) and dibromostyrene (DBS), which have the following structures:

Commercially, TBBPA and DBS are typically not used in their monomeric form, but are converted into an oligomeric or polymeric species. One class of oligomers is the brominated carbonate oligomers based on TBBPA. These are commercially available from Chemtura Corporation (examples include Great Lakes BC-52™, Great Lakes BC-52HP™, and Great Lakes BC-58™) and by Teijin Chemical (FireGuard 7500 and FireGuard 8500). These products are used primarily as flame retardants for polycarbonate and polyesters.
Brominated epoxy oligomers, based on condensation of TBBPA and epichlorohydrin, are commercially available and sold by Dainippon Ink and Chemicals under the Epiclon® series, and also by ICL Industrial Products (examples are F-2016 and F-2100) and other suppliers. The brominated epoxy oligomers find use as flame retardants for various thermoplastics both alone and in blends with other flame retardants.
Another class of brominated polymeric flame retardants based on TBBPA is exemplified by Teijin FG-3000, a copolymer of TBBPA and 1,2-dibromoethane. This aralkyl ether finds use in ABS and other styrenic polymers. Alternative end-groups, such as aryl or methoxy, on this polymer are also known as exemplified by materials described in U.S. Pat. No. 4,258,175 and U.S. Pat. No. 5,530,044. The non-reactive end-groups are claimed to improve the thermal stability of the flame retardant.
TBBPA is also converted into many other different types of epoxy resin copolymer oligomers by chain-extension reactions with other difunctional epoxy resin compounds, for example, by reaction with the diglycidylether of bisphenol A. Typical examples of these types of epoxy resin products are D.E.R.™ 539 by the Dow Chemical Company, or Epon™ 828 by Hexion Corporation. These products are used mainly in the manufacture of printed circuit boards.
DBS is made for captive use by Chemtura Corporation and is sold as several different polymeric species (Great Lakes PDBS-80™, Great Lakes PBS-64™, and Firemaster CP44-HF™) to make poly(bromostyrene) type flame retardants. These materials represent homopolymers or copolymers. Additionally, similar brominated polystyrene type flame retardants are commercially available from Albemarle Chemical Corporation (Saytex® HP-3010, Saytex® HP-7010, and PyroChek 68PB). All these polymeric products are used to flame retard thermoplastics such as polyamides and polyesters.
Unfortunately, one of the key drawbacks of the existing brominated polymer materials is their relatively low bromine content, which makes them less efficient as a flame retardant and consequently typically has a negative effect on the desirable physical properties of the flame retardant formulations containing them, such as impact strength. For example, whereas deca and deca-DPE contain 82-83% bromine, oligomers or polymers based on the brominated monomers mentioned above generally have a bromine content in the range of 52% -68%, depending on the material. This therefore typically requires a flame retardant loading level in a polymer formulation significantly higher than that required for deca, often resulting in inferior mechanical properties for the formulation.
Other considerations also influence the impact the flame retardant has on the final properties of the formulated resin. These considerations include the flame retardant thermal stability and the compatibility with the host resin. In situations where these other considerations are relatively constant, the bromine content, and hence flame retardant load level, has a major influence on the properties of the overall formulation.
To address the need for flame retardant materials that to not detract from the mechanical properties of the target resin, we have now developed a family of materials that can be classified as halogenated, and particularly brominated, aryl ether oligomers. In particular, we have found that the use of these halogenated aryl ether oligomers results in superior mechanical properties in resins such as HIPS and polyolefins and that the materials also provide excellent properties in engineering thermoplastics such as polyamides and polyesters. The aryl ether oligomers can be halogenated to a higher level than the oligomers and polymers that are commercially available today, which should have a positive effect on their mechanical property performance. It is also found that these aryl aryl ether oligomers, even at lower levels of halogenation, give formulations with acceptable mechanical properties.
Japanese Unexamined Patent Application Publication 2-129,137 discloses flame retardant polymer compositions in which the polymer is compounded a with halogenated bis(4-phenoxyphenyl)ether shown as follows:
in which X is a halogen atom, a and d are numbers in the range of 1-5, and b and c are numbers in the range of 1-4. However, the flame retardant is produced by brominating the bis(4-phenoxyphenyl)ether as a discrete compound and not an oligomeric material obtained by polymerizing an aryl ether monomer. In contrast, employing a material having an oligomeric distribution is believed to improve its performance properties as a flame retardant.
U.S. Pat. No. 3,760,003 discloses halogenated polyphenyl ether flame retardants having the general formula:
wherein each X is independently Cl or Br, each m is independently an integer of 0 to 5, each p is independently an integer of 0 to 4, n is an integer of 2 to 4, and 50% or more by weight of the compound is halogen. The ether precursors again appear to be discrete non-polymeric materials and are halogenated by reaction with bromine in the presence of iron powder as a catalyst and optionally methylene bromide. After the reaction is complete, the excess bromine is flash vaporized, leaving behind the desired solid product.
In an article entitled “Synthesis and Stationary Phase Properties of Bromo Phenyl Ethers, Journal of Chromatography, 267 (1983), pages 293-301, Dhanesar et al disclose a process for the site-specific bromination of phenyl ethers containing from 2 to 7 benzene rings. Again the ethers appear to be discrete compounds with no oligomeric distribution and, although the products are said to be useful in the separation of organic compounds, no reference is given to their possible use as flame retardants.
United States Patent Application Publication Number US 2008/0269416, which corresponds to International Publication Number WO 2008/134294, describes a halogenated aryl ether oligomer that comprises the following repeating monomeric units:
wherein R is hydrogen or alkyl, especially C1 to C4 alkyl, Hal is halogen, normally bromine, m is at least 1, n is 0 to 3 and x is at least 2, such as 3 to 100,000, for example 5 to 20. These oligomers may be prepared by brominating an intermediate oligomer composition. In Example 8 of US 2008/026416 and WO 2008/134294, the intermediate oligomer composition is prepared by an Ullmann ether reaction of resorcinol and 1,4-dibromobenzene in a 1:1 molar ratio and in the presence of a cuprous iodide (i.e. CuI) catalyst. In Example 9 of US 2008/0269416 and WO 2008/134294, the intermediate oligomer composition is prepared by oligomerizing 3-bromophenol. In Example 10 of US 2008/0269416 and WO 2008/134294, the intermediate oligomer composition is prepared by oligomerizing 4-bromophenol.
In our co-pending U.S. Provisional Patent Application No. 61/139,282, filed Dec. 19, 2008, we have described a flame retardant blend comprising at least first and second halogenated phenyl ethers having the general formula:
wherein each X is independently Cl or Br, each m is independently an integer of 1 to 5, each p is independently an integer of 1 to 4, n is an integer of 1 to 5 and wherein the values of n for the first and second ethers are different. Bromination is conveniently effected by adding bromine to a solution of the blended ether precursors in dichloromethane also containing an aluminum chloride catalyst. The reaction temperature is kept at 30° C. and the HBr off-gas is captured in a water trap. After the HBr evolution subsides, the material is worked up to give the product as an off-white solid.
WO2008/156928 discloses optoelectronic polymer compositions made from brominated polyarylethers having pendant carbazolyl groups. Useful polyarylethers are made by nucleophilic displacement condensation reactions between bisphenols and dihalogenated monomers. The resultant polyarylethers are then subjected to electrophilic aromatic substitution with bromine followed by nucleophilic aromatic substitution with a carbazole compound. Bromine substitution is typically effected by adding bromine dropwise to a solution of the ether in chloroform followed by precipitation with methanol.
The synthesis of aryl ethers via the Ullmann ether reaction has been reviewed quite extensively and has been known for over 100 years. Articles on this subject include Ley, S. V. and Thomas, A. W. Angew. Chem. Int. Ed. 2003, 42, 5400-5449; Sawyer, J. S. Tetrahedron, 2000, 56, 5045-5065; Lindley, James Tetrahedron, 1984, 40(9), 1433-1456; and Frlan, R. and Kikelj, D. Synthesis, 2006, 14, 2271-2285. The vast majority of information on this subject deals with making diaryl ethers from aryl halides and phenoxides and only a very small portion covers any research on making polymers or oligomers using this technology. In a 1945 review by Ungnade, H. E. Chemical Reviews, 1946, 38, 405-414; citing Staudinger, H. and Staiger, F. Ann. 1935, 517, 67, it was disclosed that small-chain oligomer type aryl ethers were made from a stepwise build-up using the appropriate aryl halide and phenoxide. In this case, for example, the authors used the reaction of a 4-ring α,ω-dibromo aryl ether with potassium phenoxide to make a six-ring aryl ether species. Other small-chain oligomers made in this fashion have also been reported by Hammann, W. C. and Schisla, R. M. J. Chem. Eng. Data 1970, 15(2), 352-355.
The preparation of polymers or oligomers of aryl ethers has generally been done by either homopolymerization of a halophenol, or co-polymerization of an aryldihalide with an aryldiphenol. One of the earlier works done on the polymerization of bromophenol using Ullmann chemistry was by Stamatoff (DuPont), as described U.S. Pat. No. 3,228,910 and FR 1,301,174. In these patents, it was mentioned that the reaction was conducted in an inert solvent in which sodium phenate is soluble. In this case they used such solvents as dimethylacetamide, m-dimethoxy benzene, or nitrobenzene. The catalyst was a cuprous chloride—pyridine complex. In 1968, van Dort, et al, as described in van Dort, H. M., et al European Polymer Journal, 1968, 4, 275-287, made a polymer from para-bromophenol under Ullmann conditions by reacting the sodium salt of the phenol using a cuprous chloride—pyridine catalyst complex in dimethoxybenzene at temperatures up to 200° C. Another polymerization synthesis using p-bromophenol was from Jurek and McGrath, as described in Jurek, M. J. and McGrath, J. E. Polymer Preprints 1987, 28(1), 180-1. In this case they used a cuprous chloride—quinoline complex as the catalyst with benzophenone as the solvent and used reaction temperatures up to 210° C. They also used an azeotrope solvent, such as toluene, to remove the water formed during the reaction of bromophenol with base. Once the phenate was formed and the water was removed, the toluene was stripped from the reaction to allow the polymerization to proceed at the high temperatures required.
Access to aryl ether oligomers having meta-substitution by this route is not as easy, since the meta isomer for the bromphenol starting material is less available than the para isomer of bromophenol. The alternative approach of embodiments described herein can lead to meta substitution more easily, since, in the case of resorcinol, that material is already meta-substituted.
A series of papers appear from Keller, et al, regarding the formation of aryl ether oligomers by reactions of aryldihalides with aryldiphenols. These papers include Dominguez, D. D. and Keller, T. M. High Performance Polymers 2006, 18, 283-304; Laskoski, M.; Dominguez, D. D. and Keller, T. M. J. Polym. Sci. A: Polym. Chem. 2006, 44, 4559-4565; and Laskoski, M.; Dominguez, D. D. and Keller, T. M. Polymer 2006, 47, 3727-3733. The main focus of these publications is to make thermosetting cyanate ester or phthalonitrile based resins in which the reactive monomer groups are separated by aryl ether spacer groups. In the aryl ether synthesis, they use a process in which a diphenol (such as resorcinol) is reacted with an aryldihalide (such as 1,3-dibromobenzene) in a solvent system similar to that described above using toluene and DMF, where the toluene is used to azeotrope any water formed in the reaction. They use either cuprous iodide—1,10-phenanthroline or a triphenylphosphine—copper bromide complex as the catalyst system with potassium carbonate as the base. In all cases, the reactions were run with excess of the diphenol, so the oligomer that is formed would have reactive end groups for the next step in the synthesis. They showed that in this solvent system, they could use the potassium carbonate base instead of the more expensive cesium carbonate system developed by Buchwald and co-workers 10 years earlier, as described in Marcoux, J. F.; Doye, S. and Buchwald, S. L. J. Am. Chem. Soc. 1997, 119, 10539. One of the drawbacks in using a carbonate base for the reaction is that the excess solid base that is used would need to be dealt with in some fashion during product workup. Depending on the reaction concentration, the solid bases may also create problems in handling the resulting thick slurry. Two patents to Keller, et al, i.e. U.S. Pat. No. 6,891,014 B2 and U.S. Pat. No. 6,756,470 B2, also describe reactions run with an excess of diphenol to form oligomers with reactive hydroxyl end groups as intermediates for the preparation of desired oligomeric hydroxyl arylether phthalonitrile end products. However, these patents also mention that diphenols may be reacted with dihalobenzene in a 1:1 molar ratio or with the dihalobenzene in molar excess of the diphenol. In particular, it is stated at column 6, lines 16-20 of U.S. Pat. No. 6,891,014 B2 and at column 6, lines 32-35 of U.S. Pat. No. 6,756,470 B2 that a 2:1 molar ratio of m-diiodobenzene and hydroquinone would react to form oligomers, where the average chain has three benzene rings.
Other examples are found in the literature where aryl ether oligomers are prepared from reaction of diphenolics with aryldihalides. In a report by Lindley, et al, in 1985, i.e. Lindley, P. M.; Picklesimer, L. G.; Evans, B.; Arnold, F. E. and Kane, J. J. Arylether Sulfone Oligomers with Acetylene Termination from the Ullmann Ether Reaction, in ACS Symp. Ser. 282, Ch. 3, 1985, 31-42, potassium carbonate was used either in pyridine with cuprous iodide or in collidine with cuprous oxide. It was mentioned that formation of oligomers with more than three benzene rings could be minimized by using a large excess of the aryldibromide. Lindley further reports that the chain length for the formation of the aryl ether oligomers can be controlled by adjustment of the reaction stoichiometry. See Hedberg, F. L.; Unroe, M. R.; Lindley, P. M. and Hunsaker, M. E. Wright Patterson Air Force Base Technical Report AFWAL-TR-85-4041, 1985. Oligomers were obtained using resorcinol and 1,3-dibromobenzene at 1:10 and 1:2 mol ratios. In the single reaction where the molar ratio of resorcinol to 1,3-dibromobenzene was 1:2, the percent yield was reported as 49 wt %.
A U.S. patent by Famham, et al, i.e. U.S. Pat. No. 3,332,909, discloses that polyarylene polyethers can be made from reaction of a dihydric phenol with a dibromobenzenoid compound. They mention that an alkali metal hydroxide can be used to form the metal salt of the dihydric phenol and that the water formed in the reaction can be removed with the aid of an azeotropic solvent, such as toluene, with the main solvent being benzophenone and the catalyst being a cuprous salt, such as cuprous chloride—pyridine complex. In a 1989 patent, i.e. U.S. Pat. No. 4,870,153, Matzner, et al, discloses synthesis of poly(aryl ether) polymers by a similar approach using a cuprous halide catalyst as a pyridine complex in a solvent like benzophenone with reaction temperatures in the 180-220° C. range. Both authors also employ adding a monofunctional compound, such as bromobenzene toward the end of the reaction to endcap any residual phenolic species and also mention that the stoichiometry for the two reactants needs to be within 5% of 1:1, or the molecular weight would be significantly reduced.
In a 1998 paper, i.e. Lee, J. I.; Kwon, L. Y.; Kim, J.-H.; Choi, K.-Y. and Suh, D. H. Die Angewandte Makromolekulare Chemie 1998, 254, 27-32, Lee, et al discusses polymer formation using a CuCl-pyridine complex in N-methyl-2-pyrrolidone (NMP) with either potassium carbonate or NaOH as the base and using toluene as the azeotropic solvent for water removal.
The approaches discussed above require reaction times of near 24 hr to complete the reaction or reaction temperatures near 200° C. It would, therefore, be desirable to improve the catalyst system or solvent system that is used.
It would appear that improvements in copper catalyst systems for the Ullmann ether reaction have been occurring more frequently in the last 20 years in the reactions of various monohalo benzenes with certain phenols to make simple aryl ethers. The catalysts used in the vast majority of reports are cuprous salts. In a mechanistic paper, i.e. Weingarten, H. J. Org. Chem. 1964, 29, 3624-3626, involving such catalysts, it was mentioned that cupric species get converted into cuprous species during the reaction and that cuprous is the active catalytic species. A Great Britain patent, i.e. Wedemeyer, K. and Adolphen, G. GB 1,415,945 (1975), discussed using cupric oxide, cuprous oxide, cupric bromide, or cuprous bromide, etc., in the synthesis of small aryl ether molecules by reaction of a chlorophenol with excess dichlorobenzene. They needed to use a deficit of base to achieve reasonable yields in the reaction and needed about 30% of free phenol to be present to achieve the maximum 70-75% yield.
Advantages of using a cupric salt vs. cuprous in the Ullmann reaction of aryl ether oligomers or polymers do not appear to be described in the published literature. The molecular weights of cupric oxide, cuprous oxide and cuprous iodide are 79.55, 143.1, and 190.5 g/mol, respectively. Hence, at equivalent mole ratios, less cupric oxide is required.
One of the important factors affecting the progress of the Ullmann ether synthesis is the selection of the appropriate ligand system. A recent study, published in Chang, J. W. W. et al Tet. Lett. 2008, 49, 2018-2022, on the reaction to make diaryl ethers without added ligand using phenol and iodobenzene showed that 10% CuI catalyst was needed to achieve yields above 95% and the reaction required 22 hr. Using bromobenzene or less catalyst significantly reduced the yield. In another study, published in Williams, A. L.; Kinney, R. E. and Bridger, R. F. J. Org. Chem. 1967, 32, 2501-2505, using resorcinol as the reactant with bromobenzene, Williams showed that the complexing ability of the ligands and the solvent has a significant effect on the course of the reaction. The reaction in pyridine gave 70% yield, whereas the reaction in 91% pyridine/9% 2,2′-bipyridine gave only 31% yield. They interestingly mentioned that excess base in the reaction destroys the catalyst and that they ran the reactions using 95% of stoichiometric base.
There are some other reports on the effects of ligands on the Ullmann ether reaction. Goodbrand, in Goodbrand, H. B. and Hu, N.-X. J. Org. Chem. 1999, 64, 670-674, showed that in the Ullmann reaction for amine synthesis 1,10-phenanthroline added at 3.5% with 3.5% cuprous chloride gave a significant rate acceleration to the reaction. A variety of other ligand studies can be found in the literature, including, for example, Rao, H. et al Chem. Eur. J. 2006, 12, 3636-3646; Wang, B.-A. et al Chinese J. Chem. 2006, 24, 1062-1065; Ma, D. and Cai, Q. Org. Lett. 2003, 5, 3799; Cristau, H.-J. et al Org. Lett. 2004, 6(6), 913-916; Ghosh, R. and Samuelson, A. G. New J. Chem. 2004, 28, 1390-1393. Some of the ligands mentioned include a variety of pyridine-based structures, dimethylglycine (an amino acid), 2,2,6,6-tetramethylheptane-3,5-dione, imidazoles, etc. One of the ligands, dimethylglycine (DMG) has not been used in the synthesis of polymers or oligomers.